Lignin reinforced rubber and method of making same



April 27, 1954 A. POLLAK 2,676,931

LIGNIN'REINFORCED RUBBER AND METHOD OF MAKING SAME Original Filed July 12, 1947 3 Sheets-Sheet l TENSILE STRENGTHS F LIGNIN AND CARBON BLACK FOR EQUAL VOLU/ft' LOAD/N65 GR-S 1 LBS PER SQUARE l/vcl/ EPC f\ 3000 H/YF O I00 I25 VOLUME 0F P/G/YE/VT PER /00 PARTS 619-5 7 PERCf/V? Z EL OIV/l 7/0 500 \519; f/MF 4 200 a INVENTOR NI Aer/me FULL/1K a 6 o 25 so 75 I00 W 1 0; u/w-zs a ms/151w PEE MOP/m7; OFGR-S ATTORNEYS April 27, 1954 PQLLAK 2,676,931

LIGNIN REINFORCED RUBBER AND METHOD OF MAKING SAME Original Filed July 12, 1947 3 Sheets-Sheet 2 TEAR R ES'IST'ANCES OF UGNIN ANDCARBON BLACKS EQUAL VOLUME LOAD/IVGS-G/v? -s h 600 /ua/w/v 40o m /\\HHF I 954-15. sRF zoo SHORE 14 "/m RDA/E58 us/vllv loo pc Bo SRF fpcx HHF H/VF- 6O VOLUME 0F PIG/VENT PEI? I00 PARTS OF GR-S L P47? SQUARE INCH 2000 INVENTOR 50 40 30 20 l0 0 ART/IVE 904 44k L/GNl/V, 85 PER IOOlBS GR-S l I BY v o no 20 so 40 5o WI mesa/v BLACK, zaspne /oo1.5s GR- s ATToRNF-Ys A. POLLAK April 27, 1954 LIGNIN REINFORCED RUBBER AND METHOD OF MAKING SAME 3 Sheets-Sheet 3 Original Filed July 12, 1947 92R we: 2 ii M W M o W n .w. a o

O 5 a. hwdku I IIIIII III|I PROPERTIES OF GR-S AT 77VOLUME LOADING AHL'iI ZZFMK IIIIII IIIIIII PROPERTIES OFGR-S WITH wmmm 38.5 VOLUME LOADING LIGNIN 0F LIGNIN. BY

ATTO RN EYS 7 Patented Apr. 27, 1954 LIGNIN REINFORCED RUBBER, AND METHOD OF MAKING SAME Arthur Pollak, New York, N. Y., assignor to West Virginia Pulp and Paper Company, New York, N. Ya, a corporation of Delaware Original application July 12,,194'1, Serial- No.

760,634, now Patent No. 2,608,537, dated August 26, 1952.

Divided and this application June 1952", Serial No. 291,915

6 Claims.

latex, the simultaneous precipitation of the two" latex. The principal synthetic rubbers are the copolymer of butad-i-ene and styrene (GR-SJ, the copolymer of butadiene and acrylonitrile (GR-A); and the polymer of chlorobutadiene (GR-M):

As set forth inmy parent application, I- have d scovered that certain improved results attend the use of l-igninas a reinforcing agent when the lignin is associated with the rubber as by being copreci pitated therewith from a mixture of an alkaline solution of the lignin and alatexof the rubber. Among these results may be mentionedthe compatibility of lignin with the other reinforcing agents as will be hereinafter apparent.

In case of carbon black, it is my discovery" that an unusual result occurs when lignin' and carbon black: are both present as reinforcing agents especially in the loading range of 50 parts reinforcing agent to 160' parts rubber. When the lignin'. is present in the proportion of about 2 parts to about 16' parts (the carbonblack beingpresent in the proportion of 4&8 parts to parts), the tensile strength is found to be greater than when the elastomer is loaded with parts of: carbon black alone.

A further feature of my invention has to do with the making up of a master batch of rubberlignin coprec'ipitate containing a greater amount of lignin than is required in use and thereafter incorporating in the batch further amounts of rubber by milling so as to obtain an elastome'r having the desired" proportion of lignin.

I-tisrn-y purpose to claim these matters in this divisional application.

Among the rubber-reinforcing agents, the ligreferred to herein is unique in that it is sum zoo-17.5)

bIe in aqueous a11ia1i',.such solutions being com pati'ble with the later? emulsions in all proportions. Furthermore, it is possible to precipitate both the lignin and the rubber and other pig'- ment fronrthe mixture by use of acids inv the same pH rangeas is commonly used. in coagulating or precipitating latex alone; such precipitates cor-ttai-ning the lignin: so well dispersed in the rubber as to afford excellent reinforcing action upon compounding. and curing.

In the drawing. Figures 1 and 2 show curves having a common horizontal axis designating volumes of lignin per 100 parts (by Weight) GR-S, and indicating respectively tensile strength (Fig. 1)"and elongation at break and set after break (Fig. 2) for GR-S reinforced with lig'nin in accordance with the present invention, and with three of the common carbon blacks, namely Easy Processing Channel Black (EPC), High Modulus Furnace Black (HMF) and Semi-Reinforcing. Furnace Black (SRF). In Figure 2, the set after break is given for lign-in only.

Figure 3 shows similar curves in which the tear resistance of. lignin reinforced GR-S is compared with that of carbon black reinforced GR-S of equal volume loadings; in Figure 3A are curves hav'mg" the" same horizontal axisas Figure 3 and in which share hardness of lignin reinforced GR S and carbon black reinforced GR-S are compared for equal loadings.

Figure 4 is a curve showing tensile strength of GR S lignin-ea-rbon black mixtures.

Figures 5, 6, 7 and 8 represent various proper ties of GR-S' with 38.5 Volume loading of lignin per 100" parts by weight GR-S in accordance with our invention, in comparison with other known fillers and-reinforcing agents.

Figures 9", 10*, 11' and 12 are respectively similar to" Figures 5, 6, 7' and 8' except that 7'7 volumes load'ing'of pigment p'er'IOUparts by" weight GR-S are used. I,

The following" examples will aid in the understanding of my invention:

Preparation of a rubber-Hymn cop-recipitate or crumb A solution or lignin was first made by prepar ing a slurry of25- pounds thereof in pounds of water and then adding lQYpoun'ds of 50% caustic soda. The resulting pounds of solu-'- tion: contained 25% l'igni'n in the" form of sodium lignate.

20" pounds ofGR-S latex (*cop'olymer of buta' diene and styrene) containing anti-oxidants and ,short stop agents" having a rubber cont nt of" 5' mixture, now containing a coprecipitate of 50 Compounding the coprecipz'tate The lignin-GR-S coprecipitates of various loadings similarly prepared were compounded by the following formula, parts by weight:

GR-S 100. Lignin Variable. Zinc oxide 5. Benzothiazyl disulfide 1.5.

Copper diethyldithiocarbamate 0.6/100 lignin. Plasticizer (a pine resin, e. g.

Butac 5.

Sulfur 2.

A commercial product which is 'rosin softened with turpentine.

Specimens of such loadings, cured at 292 F. tested as follows:

Tensile Tear Re- Lignin Loading, lbs/100 lbs. GR-S Strength, sistance,

lbs/sq. in. lbs/in.

The above recipe and others that follow are so. far as the ingredients other than lignin are concerned, patterned after typical GRr-S recipes and have given a satisfactory product with the customary processing equipment. Other recipes could be devised by those skilled in the art which would be equally satisfactory.

Other results are given in the form of the curves of Figs. 1, 2, 3 and 3A in which the relationships of tensile strength, elongation at break, tear resistance and hardness are all plotted against volume loadings of GR-S of both lignin and three of the common carbon blacks. The carbon black data given in Fig. 1 are taken from Bulletin No. 3 of Godfrey L. Cabot, Lac. In Fig. 1 it will be noted that up to about 37 volumes loading, the tensile strength for lignin reinforced GR-S is somewhere between that for Easy Processing Channel Black and High Modulus Furnace Black. However, at higher loadings, e. g., up to 100 volumes, the value for lignin reinforced GRPS is substantially greater than for the carbon blacks and the value for 100 volumes lignin loading is approximately that for 25 volumes lignin loading. The tear resistance (Fig. 3) is given in respect of ASTM Die B and the curves for tear resistances are essentially simi-' lar to those for tensile strength. The Shore A hardness of the lignin compounds is somewhat 4 higher though of substantially the same magnitude.

(In the rubber trade it is common to refer to reinforcing agents in terms of volume. For example, carbon black having a specific gravity of 1.8 has a specific volume of 0.56. Lignin, having a specific gravity of 1.3 has a specific volume of 0.77. On the other hand, it is customary to refer to the rubber component by parts by weight.) In Figs. 5 to 12 are shown the properties of lignin loaded GRS as compared with loadings with other pigments Figs. 5 to 8, inclusive, referring to 38.5 volume loadings whereas Figs. 9 to 12 refer to 7'7 volumes loading, i. e., volumes of pigment to 100 parts by weight of G-RS. It will be seen from these figures that at the higher loadings the lignin has greater tensile strength than the other pigments tested, has slightly greater Shore hardness than the carbon blacks and the calcium silicate, has substantially greater crescent tear resistance than the other pigments, has greater elongation than the carbon blacks taken With a comparatively low set at break. The dificrences at 38.5 volumes while similar in most instances are not as marked.

Lignin is compatible with other rubber reinforcing agents, particularly carbon black, and in Fig. 4 the curve of tensile strength is plotted for mixtures of from 0 part lignin to parts carbon black, to 50 parts of lignin and 0 part carbon black, the total loading (by weight) always being 50 pounds, this loading being chosen because in general it is recognized that maximum tensile strengths occur around such value. It will be noted that in the region of 5 parts lignin, 45 parts carbon black, the curve reaches a maximum and has a higher tensile value than with no lignin at all. From 10 parts lignin, 40 parts carbon black to 50 parts lignin and no carbon black, the curve slopes slightly downward.

The data. given in Fig. 4 were obtained by coprecipitating the carbon black and lignin but comparable results are obtained by first coprecipitating the rubber and the lignin and then in- ;corporating the carbon black by dry milling.

However, in the case of some carbon blacks, particularly medium processing channel black and high processing channel black, the milling op eration is attended with some difiiculty so that coprecipitation of both reinforcing agents and the rubber is of substantial advantage. If desired, however, the lignin may be coprecipitated with the rubber at high loading, the product being termed a master batch and then the rubber, as for example (ER-S, added by dry milling to bring 'the proportion of lignin to that desired in the final mixture and then the carbon black added by dry milling. This method likewise gives substantially the same results as given in Fig. 4. Referring to Fig. 4, the following compounding recipe was used:

GR-S Lignin; carbon black (EPC) 50 Zinc oxide 5 Benzothiazyl disulfide 1.5

Copper diethyldithiocarbamate--- 0.6/100 lignin Plasticizer 8 Sulfur 2 Rubbers other than those originally occurring as latices, e. g. butyl, reclaimed rubber, etc. may also be dry milled into the rubber-lignin coprecipitate. The compatibility of lignin with carbon black as a reinforcing agent has been brought out in the foregoing. This compatibility extends 5 to other fillers, with the result that the reinforcing action of lignin is an additive one. This action is shown in the following data:

[Tensile strength, p. s. i.]

N Hal! All [Tear resistance, lbs./in.]

N0 Half All Pigment Lignin L'i nm Lign'iu Coated Calcium Carbonate 5 Clay Calcium Silicate...

A further advantage arises from the fact that lignin has a lower density than carbon black, i. e., 1.3 as compared with 1.8-1.9 for carbon blacks. In comparison with other fillers such as clay and calcium carbonate (specific gravity 2.6), titanium oxide '(sp./g. 3.9), zinc oxide (sp../'g. 5.6), appreciable savings in weight may be had by the use of lignin. In many applicaj tions this is a highly important consideration. For example, in a rubber tire tread stock using lignin a saving of 7% in weight results for a formula normally using parts carbon black per 100 parts rubber.

Lignin has a much lower pigmenting power than carbon black, so that with its use it is possible to produce brightly colored rubber products of high strength and of lower weight using :relatively small amounts of white or colored pig-- ments or dyes.

Where it is not desired to carry out the coprecipitation of lignin with latex in a given rubber compounding plant, the master batch of lignin-loaded rubber obtained by coprecipitation, as above mentioned, may be supplied the compounder, who thereupon breaks it down and completes the compounding with additional rubber and carbon or such other mix as may be desired.

The foregoing examples involve GRI-S. The following. is an example of coprecipitating and compounding natural rubber with lignin.

Natural rubber latex containing 38.5 solids to give--- 100 parts rubber. Lignin as sodium lignate to give '50 parts lignin. Zinc oxide 5 parts. Mercaptobenzothiazole 1.5 parts. Tetramethylthiuram monosulfide 0.4 part. Stearic acid 1.0 part. Antioxidant 0.5 part. Sulfur 2.5 parts.

A sample of this compound cured for five minutes at 292 F. gave results as follows:

Tensile strength, p. s. i 3980 Modulus at 390% elongation, p. s. i 600 Elongation at break, .per cent 7'40 Tear resistance, lbs/in 770 Shore A hardness 73 The following is a similar example of com 6 pounding and coprecipitating nitrile rubber (GR/ A) with lignin:

Nitrile rubber latex containing .26 mol ,per cent acrylo- A sample of this compound cured for 60 minutes at 292 F. gave the following tests:

Tensile strength, p. s. i 3100 Modulus at 300% elongation, p. s. i 630 Elongation at break, per cent- '660 Tear resistance, lbs./in '160 Shore A" hardness 74 In both of the examples last given the rubber was coprecipitated with the lignin in the same manner as in the case of the GR-S lignin coprecipitates previously given.

As expected the tensile strength and tear resistance of natural rubber is somewhat higher than in the case of GR-S for the same loadings (38.5 volume loading of lignin being the same as '50 parts by weight). The use of lignin, with other synthetic rubbers, as for example neoprene (GR-M) is also advantageous.

When the so-called wet crumb, i. e., the filter cake from the operation of filtering the lignin rubber coprecipitate, is milled in known devices (PlasticatonColloid Mill, Banbury mixer or roller mill) the lignin is caused to undergo an even further subdivision in particle size due to the shearing action which takes place in the gelled lignin particles. If desired, advantage may be taken of this shearing action by adding gelled lignin to the mixture during the milling operation. Lignin in the gelled state is available (1) from the lignin prepared from black liquor prior to drying, (2.) by soaking or grinding dried lignin with suflicient alkaline solution or other solvent,

i. e.,dio'xa ne, ethylene glycol, etc., to give a paste,v

or (3) the-lignin may be mixed with a .sufiicient quantity of fugitive alkali such as ammonia or morpholine, or a polymerizable chemical such as aniline or ahiline-furfural mixture, with 'sufilcient agitation or trituration, or with other agents, as for example reactable chemicals (toluidine, cresol). Rubber plasticizers, e. g. diethylene glycol, coal tar bases, capable of gelling with lignin may also be employed for this purpose and a lignin gel formed in the same way, i. e., trituration, agitation, etc. However formed, the lignin gel as such, or mixed with other pigment or plasticizer may be milled with the rubber along with other agents, e. g., other reinforcing agents, pigments, accelerators, curing agents, etc. In this manner the lignin or lignin-pigment mixture is dispersed in the rubber and the lignin subdivided into particle size to give a reinforcing effect comparable with that obtained by coprecipitation with the rubber. Such action, however, is to .be .distinguished from the us of dried precipitated lignin which is generally of large particle size, about one to .five microns, and does not give reinforcing action which is comparable with either carbon black or coprecipitated lignin. when polymerizable or reactable chemicals have been used to gel the lignin they will, under ouring, polymerize or react and to some extentserve as a reinforcing agent and filer for the rubber. In the case of a volatilizable alkali, e. g morpholine, this will be volatilized during the curing and to some extent during the milling.

Since the lignin is slightly acidic in nature,.its presence retards somewhat the cure where the usual alkaline accelerator chemicals such as diphenyl guanidine or mercaptobenzothiazole are used. This may be readily overcome by the use of more or stronger accelerator chemicals, such as copper diethyldithiocarbamate or tetramethylthiuram monosulfide, or by increasing the amount of a base present, as by increasing the quantity of the zinc oxide. r the acidity may be reduced by adding alkalis, alkaline substances such as amines, or compounds or groups I, II, and III metals such as lime which form salts with lignin. These may be added either while milling or preferably to the wet coprecipitate of lignin and rubber.

Advantage may be otherwise taken of the property of lignin of being soluble in and gelling in alkaline solutions in order to form a dispersion of it with rubber latex. For example, the lignin may b added to the latex as a wet slurry and a thorough mixture obtained by agitation. Where, as is usual, the pH of the latex is on the alkaline side, the lignin, which has an acid reaction, will dissolve and cause a drop of the pH to a point where the rubber and lignin will precipitate. Furthermore, such of the lignin, if any, as does not precipitate will be gelled under these condi tions and in this form will be readily subdivisible and dispersible in the milling operation, as has already been pointed out. If necessary the pH of the mixture may be adjusted to the desired point to completely precipitate the rubber or the rubber and lignin mixture. Even dry lignin when mixed with latex under these conditions will similarly become either dissolved or gelled. Other alkalis than the alkali metal hydroxides may be used to solubilize the lignin, as for example ammonia, triethanolamine, diethanolamine, etc.

While acids are commonly used for forming the lignin-latex coprecipitates, their coprecip-ita tion can be induced by other means. Thus, a fugitive alkali such as ammonia, morpholine or polymerizable amines, e. g., aniline, may be used to solubilize the lignin; and then, after addition of the solution to the latex, coprecipitation may be induced by heating. This effect may also be aided by the addition of electrolytes. Coprecipitation may also be induced by either freezing or evaporation.

Additionally, the electrolytic decomposition of latex-lignin dispersions or solutions is likewise practical.

Lignin is generally identified as that component of wood which is insoluble in 72% H2304; it is a compound of carbon, hydrogen and oxygen, and sometimes of the foregoing plus sulfur, and is further characterized by being soluble: in solvents such as dioxane and by having sufficient acidity so that it will combine with sodiumor nitrogen alkalis, and form water soluble compounds which can be precipitated by adding acids. In sulfite cooking the lignin of the wood is rendered soluble by the action of the wood with cooking liquors. These extracts of the wood either as such or partly purified are sometimes mistakenly termed lignin but are actually lignin sulfonates. It is possible to treat lignin washing. The lignin so made is a dry powder having the following range of analysis:

Moisture 4%.

Ash Less than 0.5%. Sulfur l2%. Methoxyl l3.5-1-i.5%. Dioxane insolubles Less than 1%.

A still further source of lignin suitable for the purpose of the present application is the saccharification of the wood and other ligneous vegetable matter, e. g., the Scholler process and its modifications, which produces an insoluble ligneous residue which is highly acidic, containing some sugars, hemicelluloses and other degradation products of cellulose. This material is susceptible to purification to yield a material suitable for coprecipitation with rubber.

The product of this application is termed an elastomer by which is meant a composition having theability to stretch, upon the application of stress, from 200 to 300% or more of its original length, and after release of the stress to return to essentially its originalv length. The curves, particularly Figs. 2, 8 and 12, illustrate this property. In general, it will be seen that throughout the loading up to volumes the elastomer produced conforms to this definition. It is recognized, however, that for most rubber uses known today, the optimum properties are not developed until quantities of reinforcing agent in excess of 10 volumes percent have been incorporated as can be seen from an examination of Figs. 1, 2, 3 and 3A.

In the claims it will be understood that rubber is-intended to include both natural and synthetic rubber originally occurring as an aqueous alkaline emulsion unless the contrary is indicated.

I claim:

1. An elastomer comprised of polymeric butadiene rubber and a reinforcing agent in proportions of substantially 50 parts by weight of the reinforcing agent for 100 parts by weight of rubber, the reinforcing agent comprising carbon black and a substantial proportion of lignin from about 2 to about 10 parts, said elastomer having a tensile strength greater than that for 50 parts "of carbon black alone, said elastomer being produced by steps which comprise coprecipitating the mixture of a latex of the rubber and an alkaline solution of the lignin, drying the coagulum so produced, masticating and softening and effecting breakdown of the same with the lignin and carbon black substantially uniformly dispersed throughout the rubber.

2. An elastomer comprised of butadiene styrene copolymer and a reinforcing agent in proportions of substantially 50 parts by weight of the agent for 100 parts by weight of polymer, the reinforcing agent comprising carbon black and a substantial-proportion of lignin from about 2 to about 10 parts, the elastomer having a tensile strength in excess of 3000 p. s. i., said elastomer being produced by steps which comprise coprecipitating the mixture of a latex of the rubber and an alkaline solution of the lignin, drying the coagulum so produced, masticating and softening and effecting breakdown of the same with the lignin and carbon black substantially uniformly dispersed throughout the rubber.

3. An elastomer comprised of polymeric buta diene rubber and a reinforcing agent in proportions of substantially 50 parts by weight of the agent for 100 parts by weight of rubber, the agent comprising carbon black and a substantial proportion of lignin from about 2 to about 10 parts of lignin to 48 to 40 parts of carbon black, said elastomer being produced by steps which comprise coprecipitating the mixture of a latex of the rubber and an alkaline solution of the lignin, drying the coagulum so produced, masticating and softening and effecting breakdown of the same with the lignin and carbon black substantially uniformly dispersed throughout the rubber.

4. The method of making a reinforced elastomer' which comprises mixing aqueous alkali lignate and a latex of a polymeric butadiene rubber, coprecipitating the rubber and lignin to produce a coagulum containing the rubber and lignin, drying the coagulum, masticating and softening and effecting breakdown of the same to form a reinforced elastomer having the lignin substantially uniformly dispersed therethrough in amounts greater than those required in use and thereafter milling said elastomer and adding additional uncured rubber during the milling.

5. The method according to claim 4 in which additional reinforcing agent in the form of carbon black is added by milling.

0. A reinforced elastomer produced by the method of claim 4.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,355,180 Remy Aug. 8, 1944 2,575,061 McMahon Nov. 13, 1951 

1. AN ELASTOMER COMPRISED OF POLYMERIC BUTADIENE RUBBER AND A REINFORCING AGENT IN PROPORTIONS OF SUBSTANTIALLY 50 PARTS BY WEIGHT OF THE REINFORCING AGENT FOR 100 PARTS BY WEIGHT OF RUBBER, THE REINFORCING AGENT COMPRISING CARBON BLACK AND A SUBSTANTIAL PROPORTION OF LIGNIN FROM ABOUT 2 TO ABOUT 10 PARTS, SAID ELASTOMER HAVING A TENSILE STRENGTH GREATER THAN THAT FOR 50 PARTS OF CARBON BLACK ALONE, SAID ELASTOMER BEING PRODUCED BY STEPS WHICH COMPRISE COPRECIPITATING THE MIXTURE OF A LATEX OF THE RUBBER AND AN ALKALINE SOLUTION OF A LIGNIN, DRYING THE COAGULUM SO PRODUCED, MASTICATING AND SOFTENING AND EFFECTING BREAKDOWN OF THE SAME WITH THE LIGNIN AND CARBON BLACK SUBSTANTIALLY UNIFORMLY DISPERSED THROUGHOUT THE RUBBER.
 4. THE METHOD OF MAKING A REINFORCED ELASTOMER WHICH COMRISES MIXING AQUEOUS ALKALI LIGNATE AND A LATEX OF A POLYMERIC BUTADIENE RUBBER, COPRECIPITATING THE RUBBER AND LIGNIN TO PRODUCE A COAGULUM CONTAINING THE RUBBER AND LIGNIN, DRYING THE COAGULUM, MASTICATING AND SOFTENING AND EFFECTING BREAKDOWN OF THE SAME TO FORM A REINFORCED ELASTOMER HAVING THE LIGNIN SUBSTANTIALLY UNIFORMLY DISPERSED THERETHROUGH IN AMOUNTS GREATER THAN THOSE REQUIRED IN USE AND THEREAFTER MILLING SAID ELASTOMER AND ADDING ADDITIONAL UNCURED RUBBER DURING THE MILLING. 